In a scanning tunneling microscope as disclosed in U.S. Pat. No. 4,343,993, a tip is required to be sharpened to observe the sample surface with atomic-resolution. In recent years, therefore, the tip has been machined and sharpened by electropolishing so that the fine tip is constituted of only one atom.
When a sample is observed with a scanning tunneling microscope, it is necessary to reduce the distance between the tip and the sample surface to about 1 nm to obtain a tunneling current between the tip and the sample surface. When the tip is being brought close to the sample surface, the tip may come into contact with the sample. As a result, the front end of the tip or the sample may be damaged. If the front end of the tip is damaged, it is impossible to obtain atomic-resolution and, therefore, it is necessary to replace the tip with a new one. If the sample is damaged, it is necessary to replace it with a new sample or change specimen position.
However, skill is needed to replace such a fine tip. Also, replacement of the tip and the sample can only be performed after breaking the ultrahigh vacuum in the vacuum vessel accommodating the tunneling microscope. Thus, it takes a long time to restart the observation.
Before surface analysis is made with a scanning tunneling microscope, it is necessary to clean the sample surface. For this purpose, the sample is heated at about 1200.degree. C. to remove contaminants from the sample surface, or the surface is treated by ion sputtering or another method. When the sample surface is treated in this way, the contaminants evaporating from the sample may adhere to the tip, or the tip may be damaged by heat radiating from the sample.